Tin-containing composition and use

ABSTRACT

A tin-containing composition is provided, the composition having a tin Auger line transition wherein the ratio of the area of the M 5  N 4 ,5 N 4 ,5 transition peak at 424.5 eV±1 eV, having a 6 eV FWHM, to the area of M 4  N 4 ,5 N 4 ,5 transition peak at 430.5 eV±1 eV is at least 10 to 1. Additional such tin-containing compositions, including catalyst compositions are also provided as are methods for converting feedstock alkanes containing from 1 to 4 carbon atoms to higher molecular weight hydrocarbons using such catalyst compositions.

This is a division of application Ser. No. 382,477, filed July 19, 1989,now U.S. Pat. No. 4,971,940 which is a CIP of Ser. No. 233,063, filedAug. 17, 1988, now U.S. Pat. No. 4,934,311, all of whose disclosures areincorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to novel tin-containing compositions and theiruse.

As the uncertain nature of ready supplies and access to crude oil hasbecome increasingly apparent, alternative sources of hydrocarbons andfuel have been sought out and explored. The conversion of low molecularweight alkanes (lower alkanes) to higher molecular weight hydrocarbonshas received increasing consideration as such low molecular weightalkanes are generally available from readily secured and reliablesources. Natural gas, partially as a result of its comparativeabundance, has received a large measure of the attention focused onsources of low molecular weight alkanes. Large deposits of natural gas,and mainly composed of methane, are found in many locations throughoutthe world. In addition, low molecular weight alkanes are generallypresent in coal deposits and may be formed during numerous miningoperations, in various petroleum processes, and in the above- orbelow-ground gasification or liquefaction of synthetic fuelstocks, suchas coal, tar sands, oil shale and biomass, for example. In addition, inthe search for petroleum, large amounts of natural gas are discovered inremote areas where there is no local market for its use as a fuel orotherwise. Additional major natural gas resources are prevalent in manyremote portions of the world such as remote areas of western Canada,Australia, U.S.S.R. and Asia. Commonly, natural gas from these types ofresources is referred to as "remote gas".

Generally much of the readily accessible natural gas is used in localmarkets as the natural gas has a high value use as a fuel whether inresidential, commercial or industrial applications. Accessibility,however, is a major obstacle to the effective and extensive use ofremote gas. In fact, vast quantities of natural gas are often flared,particularly in remote areas from where its transport in gaseous form ispractically impossible.

Conversion of natural gas to liquid products is a promising solution tothe problem of transporting low molecular weight hydrocarbons fromremote areas and constitutes a special challenge to the petrochemicaland energy industries. The dominant technology now employed forutilizing remote natural gas involves its conversion to synthesis gas,also commonly referred to as "syngas", a mixture of hydrogen and carbonmonoxide, with the syngas subsequently being converted to liquidproducts. While syngas processing provides a means for convertingnatural gas to a more easily transportable liquid that in turn can beconverted to useful products, the step of forming synthesis gas as anintermediate is typically relatively costly as it involves adding oxygento the rather inert methane molecule to form a mixture of hydrogen andcarbon monoxide. While oxygen addition to the carbon and hydrogen ofmethane molecules may be advantageous when the desired products arethemselves oxygen containing, such as methanol or acetic acid, forexample, such oxygen addition is generally undesirable when hydrocarbonssuch as gasoline or diesel fuel are the desired products as the addedoxygen must subsequently be removed. Such addition and removal of oxygennaturally tends to increase the cost associated with such processing.

Methane, the predominant component of natural gas, although difficult toactivate can be reacted with oxygen or oxygen-containing compounds suchas water or carbon dioxide to produce synthesis gas. Synthesis gas canbe converted to syncrude such as with Fischer-Tropsch technology andthen upgraded to transportation fuels using usual refining methods.Alternatively, synthesis gas can be converted to liquid oxygenates whichin turn can be converted to more conventional transportation fuels viacatalysts such as certain zeolites.

Because synthesis gas processing requires high capital investment, withthe syngas being produced in relatively energy intensive ways, such asby steam reforming where fuel is burned to supply heat for reforming,and represents an indirect route to the production of hydrocarbons, thesearch for alternate means of converting methane directly to higherhydrocarbons continues.

Oxidative coupling has been recognized as a promising approach to theproblem of methane conversion although the mechanism of action is not,to date, completely understood. In such processes, methane is contactedwith solid materials referred to by various terms including "catalyst","promoters", "activators" or "contact materials", for example Methanemixed with oxygen and catalyst is directly converted to ethane,ethylene, higher hydrocarbons and water. Carbon dioxide formation, whichis highly favored thermodynamically, is an undesirable productassociated with oxidative coupling as both oxygen and carbon areconsumed without production of the desired higher value C₂ +hydrocarbons. In addition, many methods for oxidative conversion havebeen carried out in the absence of an oxygen-containing gas,theoretically relying on oxygen being supplied by the catalyst.

Catalytic mixtures of yttrium-barium-copper oxides are highly active and100% selective for producing CO₂. Such catalysts which are highlyselective for carbon dioxide formation are commonly referred to as"combustion catalysts". In order to obtain increased selectivity tohydrocarbon formation, Group IA metals, particularly lithium and sodium,have been added or otherwise used in many such catalytic mixtures. Underthe conditions used for oxidative coupling, however, such mixturestypically realize migration and loss of the alkali metal. Thus, the needfor highly active, C₂ + hydrocarbon selective and stable oxidativecoupling catalyst and improved processes employing the same continues.

Many patents describe processes for converting methane to heavierhydrocarbons in the presence of reducible metal oxide catalysts. Most ofthese patents require or imply the need for a separate stage tore-oxidize the catalyst. These include U.S. Pat. No. 4,444,984 whichteaches a reducible oxide of tin as a catalyst; U.S. Pat. No. 4,495,374disclosing the use of any reducible oxide promoted by an alkaline earthmetal; U.S. Pat. No. 4,523,049 showing a reducible oxide catalystpromoted by an alkali or alkaline earth metal, and requiring thepresence of oxygen during the oxidative coupling reaction. U.S. Pat. No.4,656,155 specifies yttrium in a mixture requiring zirconium and alkalimetal. U.S. Pat. No. 4,450,310 claims coupling promoted by alkalineearth oxides in the total absence of molecular oxygen. U.S. Pat. No.4,482,644 teaches a barium-containing oxygen-deficient catalyst with aperovskite structure. European Patent Application 198,251 covers aprocess conducted in the presence of free oxygen using a three componentcontact material of: a) an oxide of calcium, strontium or barium, andoptionally a material selected from the group consisting of chlorideions, compounds containing chloride ions, tin and compounds containingtin; b) a sodium or potassium-containing material, and a Group IIA metalor a compound containing a Group IIA metal, and optionally a materialselected from the group consisting of chloride ions, compoundscontaining chloride ions, tin and compounds containing tin; c) a GroupIA metal compound, and optionally a material selected from the groupconsisting of chloride ions, compounds containing chloride ions, tin andcompounds containing tin.

U.S. Pat. No. 3,885,020, although disclosing contact materials of theoxidative coupling type, is directed to a method of convertinghydrocarbons to CO₂ and water for pollution control. The combustioncatalysts used consist of four components: 1) zirconium, tin or thorium;2) an alkaline earth material; 3) a rare earth-type element such asscandium, lanthanum or cesium; and 4) a metal of the first transitionseries.

Baerns U.S. Pat. No. 4,608,449 relates to a methane conversion processusing a suitable metal oxide catalyst, including tin oxide, on an oxidecatalyst carrier carried out under temperatures of from 500° C. to 900°C. in the presence of oxygen at specified pressure.

Hicks U.S. Pat. No. 4,780,449 discloses a catalyst for the conversion ofmethane to hydrogen, and higher hydrocarbons comprising a non-reduciblemetal oxide of Be, Mg, Ca, Sr, Ba, Sc, Y, La, Pr, Nd, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb and Lu which may be used alone or with up to 50% byweight of one or more promoter oxides of Li, Na, K, Be, Mg, Ca, Sr, Ba,Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sn, Pb,Sb, Bi, Cu, Ag and Au. Methane conversion is carried out at temperaturesof from 500° to 1000° C.

Many analytical techniques have been developed to determine surfacestructure and/or composition of materials, e.g., solids. One suchtechnique which has gained widespread application is Auger electronspectroscopy wherein electrons or photons, usually of 2 to 10 KeV, areused to excite core electrons of atoms of the solid with outer shellelectrons "falling" into the electron vacancies created by the excitedinner electrons. Such de-excitation of outer electrons into innerelectron vacancies may lead to either an X-ray emission, or the energymay be given to another electron of the atom, commonly referred to asthe Auger effect. Such Auger electrons have well-defined energiesdetermined by the electron shells involved in the process, thus an Augerspectrum is characteristic of the atom and the environment about theatom. In Auger electron spectroscopy, the Auger electron is able toescape from the near surface region without appreciable energy loss;hence, the energy emission associated with such spectroscopy isprimarily associated with surface or near surface atoms. Thus, one ofthe principal uses of Auger spectra is for the determination of thesurface composition.

In general, quantum mechanics can be utilized to describe the discreteenergy levels associated with the electrons of an atom. Thus, principalquantum numbers (n=1, 2, 3, 4 . . . ) correspond to electron shells (K,L, M, N . . . , respectively). Auger notation builds on atomic electronshell notation, with subscripted numbers referring to the shell angularmomentum state involved. Thus, subscript "1" refers to the s shellangular momentum state, subscripts "2" and "3" refer to the p1/2 or p3/2shell angular momentum states, and subscripts "4" and "5" refer to thed3/2 or d5/2 shell angular momentum states, respectively, for example.

Auger transition notations are referred to by three capital letters;e.g., KLL, KLM, LMM, MNN, etc. The first letter in the notation refersto the electron shell in which the initial electron vacancy associatedwith the excitation of core electrons during Auger emission occurs,e.g., MNN indicates that the initial vacancy was in the M electronshell. The second letter in the notation refers to the shell from whichan electron comes to fill the initial vacancy; e.g., MNN indicates an Nelectron "drops" to fill the "hole" in the M electron shell. The thirdletter refers to the shell from which the Auger electron (as describedabove) is emitted or ejected; e.g., MNN indicates that the Augerelectron is expelled from the N shell.

Thus, the Auger transition notation M₄ N₄,5 N₄,5 means that the initialvacancy was in the M electron shell in the 3d3/2 state with the "hole"filled with a 4d electron from the N electron shell and a 4d electronfrom the N electron shell being expelled as the Auger electron.Conversely, the Auger transition notation M₅ N₄,5 N₄,5 is for an initialvacancy in the 3d5/2 state of the M electron shell with the same twotypes of 4d electrons involved in the Auger decay. Thus, the splittingof the two Auger features roughly would equal the spin orbit splittingof the 3d states.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome one or more of theproblems described above.

According to the invention, an oxidized tin-containing composition isprovided having a tin Auger line transition wherein the ratio of the M₅N₄,5 N₄,5 transition peak at 424.5 eV±1 eV kinetic energy, having a 6 eVfull width in eV at half maximum peak height (hereinafter referred to as"FWHM"), to the M₄ N₄,5 N₄,5 transition peak at 430.5 eV±1 eV kineticenergy is at least 10 to 1.

In one embodiment of the invention, such a tin-containing compositionadditionally including a Group IIA metal and oxygen is provided. TheGroup IIA metal preferably is magnesium, calcium, strontium or barium.In the composition, the tin and the Group IIA metal are present in anapproximate atomic ratio of 2-4 atoms of tin per 0.5-3 atoms of GroupIIA metal.

The invention also provides a process for converting a feedstock alkanecontaining from 1 to 4 carbon atoms to a higher molecular weighthydrocarbon. The process includes contacting a feedstock containing atleast one alkane containing from 1 to 4 carbon atoms with a particularoxidative coupling catalyst in the presence of oxygen at oxidativecoupling reaction conditions to produce a gaseous mixture includinghydrocarbon products having higher molecular weight than the feedstockalkane from which they were formed. The particular oxidative couplingcatalyst includes: a) a Group IIA metal selected from the groupconsisting of magnesium, calcium, strontium and barium; b) tin and c)oxygen wherein the tin and Group IIA metal are in an approximate atomicratio of 2-4 atoms of tin per 0.5-3 atoms of Group IIA metal with thecatalyst having a tin Auger line transition wherein the ratio of the M₅N₄,5 N₄,5 transition peak at 424.5 eV±1 eV, having a 6 eV FWHM, to theM₄ N₄,5 N₄,5 transition peak at 430.5 eV±1 eV is at least 10 to 1.

The invention also comprehends an oxidative coupling catalysts useful insuch a process.

As used herein, references to Auger transition spectra peak ratios areto be understood as being based on the "area under" the respective peakor peaks. Herein, the areas under the various integrated Augertransition peaks are measured by a linear background subtraction methodwith, in the case of the Sn (MNN) Auger transition, the area of the430.5±1 eV peak (the "first peak") being measured from the point ofonset of the peak rise to the minimum point between the first peak andthe 424.5±1 eV peak (the "second peak"), and the area of the second peakbeing measured in a similar fashion, from the minimum point between thefirst and second peaks to the end of the transition (roughly at 410 eVkinetic energy).

Further, references herein to energy peaks are to be understood to referto kinetic energy (standardized to correct for charging electronemission and resulting surface charge build-up of the material) and notto binding energy.

Additionally, energy scales shown in the figures and referred to hereinare those of binding energy relative to Al K₆₀ radiation at 1486.3 eV.

Also, as used herein, the term "fresh catalyst" refers to a catalystcomposition that has been calcined but has not subsequently been exposedto oxidative coupling reaction conditions, which conditions typicallyinvolve exposure at relatively high temperatures (as described laterherein) to reactants such as low molecular weight alkanes, e.g.,methane, and oxygen. Correspondingly, the term "used catalyst" refers tosuch of these compositions which have been exposed to such oxidativecoupling reaction conditions. "Overreduced" oxidative coupling catalystsare those catalysts which have been irreversibly changed due to reducingconditions.

Other objects and advantages of the invention will be apparent to thoseskilled in the art from the following detailed description taken inconjunction with the appended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the Sn (MNN) Auger spectrum of a tin-containing composition ofthe invention (A) and those of other tin-containing compositions(Xl-X4);

FIG. 2 is the Sn (MNN) Auger spectra of various oxidized tin-containingcompositions of the invention, which compositions also contain oxidizedbarium;

FIG. 3 is of Sn (MNN) Auger spectra of various oxidized tin-containingcompositions of the invention, which compositions also contain oxidizedyttrium and oxidized barium;

FIG. 4 is a ternary phase diagram, as derived by STEM/EDX, of fresh Y₁Ba₂ Sn₃ O_(y) catalyst composition;

FIG. 5 is a ternary phase diagram, as derived by STEM/EDX, of used Y₁Ba₂ Sn₃ O_(y) catalyst that has not been exposed to reducing conditions;

FIG. 6 is a ternary phase diagram, as derived by STEM/EDX, of used Y₁Ba₂ Sn₃ O_(y) catalyst that has been exposed to reducing conditions;

FIG. 7 is a ternary phase diagram, as derived by STEM/EDX, of used Y₁Ba₂ Sn₃ O_(y) catalyst that has been exposed to severe reducingconditions;

FIG. 8 is the Auger spectrum of fresh Y₁ Ba₂ Sn₃ O_(y) catalyst;

FIG. 9 is the Auger spectrum of used, overreduced Y₁ Ba₂ Sn₃ O_(y)catalyst;

FIG. 10 is the Auger spectrum which shows the typical Sn MNN transitionobserved in SnO;

FIG. 11 is the Auger spectrum which shows the typical Sn MNN transitionobserved in SnO₂ ;

FIG. 12 is the Auger spectrum which shows the typical Sn MNN transitionobserved in BaSnO₃ ; and

FIG. 13 is the Auger spectrum which shows the typical Sn MNN transitionobserved in Y₂ Sn₂ O₇.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a novel, oxidized tin-containingcomposition as demonstrated by a novel tin Auger line transition. Theoxidized tin-containing composition of the invention has a tin Augerline transition wherein the ratio of the M₅ N₄,5 N₄,5 transition peak at424.5 eV±1 eV, having a 6 eV FWHM, to the M₄ N₄,5 N₄,5 transition peakat 430.5 eV±1 eV is at least 10 to 1 and generally in the range of 10 to1 and to about 350 to 1 as will be described below.

In general, tin has found widespread use in many varying applications.More specifically, oxidized tin-containing compositions, such as formsof tin oxide, have been used in applications including as semiconductorelectrodes or liquid crystal displays or use as a flame retardant, anabrasive, an additive to porcelain used in dental work, a glass additiveto increase opacity and as a gas (e.g., carbon oxide, hydrogen andhydrocarbon) sensor. In addition, tin oxides are frequently utilized inmany catalytic applications, such as the catalytic cracking of variouslarge molecular weight petroleum feedstocks.

FIG. 1 presents the Sn (MNN) Auger spectrum of a tin-containingcomposition of the invention (A) as well as those of othertin-containing compositions (comparative compositions X1-X4). Thesecompositions as well as the methods of their preparation are describedbelow in Example 1.

As is evident in FIG. 1, the comparative tin-containing compositionsX1-X4 exhibit two peaks, one peak for the M₅ N₄,5 N₄,5 transition andthe other for the M₄ N₄,5 N₄,5 transition, with the areas under each ofthese peaks being of about the same order of magnitude. The compositionof the invention (Composition A), however, exhibits an Auger spectrumwherein the area under the M₅ N₄,5 N₄,5 transition peak greatly exceedsthe area under the M₄ N₄,5 N₄,5 transition peak.

FIG. 2 presents the Sn (MNN) Auger spectra of various tin-containingcompositions (B-E) of the invention, which compositions also containbarium and oxygen and for which compositions the method of preparationare described below (see Example 2). FIG. 3 represents the Sn (MNN)Auger spectra of composition A and various additional tin-containingcompositions (F-H) of the invention, which compositions also contain theGroup IIIB metal yttrium, the Group IIA metal barium and oxygen and forwhich compositions the method of preparation are described below (seeExample 3). Each of the compositions has a peak at 424.5 eV±1 eV, withthis peak having about a 6 eV FWHM. Typically the Sn (MNN) Auger spectraof oxidized tin, whether alone or in tin-containing compositions such asdescribed below and shown in FIGS. 8-13, exhibit a second peak at about430.5 eV, with the ratio of the area of the first peak to the secondpeak ranging from about 4.8 to about 2.2.

While the oxidized tin-containing compositions of the invention maycontain other elements or materials, the only material known to date tobe required to be present is the oxidized tin itself. Other elements ormaterials which may be present in the compositions of invention includeGroup IIA metals such as magnesium, calcium, strontium and barium.Additionally, or in the alternative, Group IIIB metals such as yttrium,lanthanum and scandium, also preferably in an oxidized form, may beincluded.

In a preferred form the composition includes a) a Group IIA metal ofmagnesium, calcium, strontium or barium (preferably barium), b) tin andc) oxygen. One such composition may be represented by the formulaBaSnO_(y) wherein y represents the number of oxygen anions required tobalance the combined charge of the cationic species Ba and Sn.

In another preferred form, the composition includes: a) Group IIIB metalselected from the group of yttrium, lanthanum, and scandium (preferablyyttrium; b) a Group IIA metal selected from the group of magnesium,calcium, strontium and barium (preferably barium); c) tin and d) oxygenwherein the tin, Group IIA metal and Group IIIB metal are present in anapproximate atomic ratio of 2-4 atoms of tin per 0.5-3 atoms of GroupIIA metal per atom of Group IIIB metal.

In a preferred form of such a composition, wherein the Group IIIB metalis yttrium and the Group IIA metal is barium, the yttrium and barium andtin are present at an approximate atomic ratio of 1:2:3, respectively,and the composition is represented by the formula Y₁ Ba₂ Sn₃ O_(y)wherein y represents the number of oxygen anions required to balance thecombined charge of cationic species Y, Ba and Sn when the cationicspecies barium is present solely as the oxide. When the cationic speciesis present as the carbonate, a preferred composition may be representedby the empirical formula Y₁ Ba₂ Sn₃ O_(y) C_(z) wherein z has a value ofup to 2, and y represents the number of oxygen anions required tobalance the combined charge of the cationic species, Y, Ba and Sn andthree times the number of carbon atoms (i.e., 3z).

A preferred composition of the invention is represented by the formula

    (Y.sub.2 O.sub.3) (BaO).sub.4-x (BaCO.sub.3).sub.x (SnO.sub.2).sub.6

wherein x is 0 when barium is present solely as an oxide and has a valueof up to 4 when some of the barium species is present as the carbonate.For best results; it is preferred that the barium be present solely asan oxide, i.e., that x=0.

Forms of the oxidized tin-containing compositions of the invention whichinclude an oxidized Group IIA metal selected from the group ofmagnesium, calcium, strontium and barium, with barium being particularlypreferred, are useful in the conversion of feedstock alkanes containingfrom 1 to 4 carbon atoms to higher molecular weight hydrocarbons.Particularly preferred for use in the conversion of such feedstockalkanes which contain from 1 to 4 carbon atoms to higher molecularweight hydrocarbons are those compositions additionally comprising anoxidized Group IIIB metal selected from the group of yttrium, lanthanumand scandium. In particular, those of these compositions wherein theoxidized Group IIIB metal comprises yttrium and the oxidized Group IIAmetal comprises barium have been found to be particularly useful forsuch conversions.

As described above, such processes are commonly referred to "oxidativecoupling" processes. Certain compositions of the invention have beenfound useful as oxidative coupling catalysts and are relatively stableat oxidative coupling conditions, thereby offering an advantage overprior art technology.

In one aspect of the invention, a method for converting a feedstockalkane containing from 1 to 4 carbon atoms to form hydrocarbon productshaving higher molecular weights than the feedstock alkane from whichthey were formed comprising contacting a feedstock with a specifiedoxidative coupling catalyst in the presence of oxygen at oxidativecoupling reaction conditions is provided. It is believed that processvariable conditions including pressure, temperature, flow rate, feed gascomposition and residence time can be widely varied within suitableparameters. Preferably, conditions should be chosen to cause oxygenconversion to proceed near to, but short of, completion in order toprotect the catalyst from possible overreduction and degradation. Thisbecomes particularly important at higher pressures and temperatureswhere increased catalytic activity may be compensated for by utilizingshorter contact times so as to avoid conditions at which complete oxygenconversion is realized. It is generally preferred to employ temperaturesof from about 700° C. to about 900° C. and relatively low pressures,preferably pressures less than about 250 psig, and most preferably atabout ambient pressure.

At temperatures up to about 800° C., residence times or relative feedrates are less critical. In operation, feed rates at room temperatureand atmospheric pressure, e.g., feed rate/catalyst rate, may be variedfrom about 1000 cc/gm-hr to about 165,000 cc/gm-hr without substantiallyaffecting catalyst performance.

The feedstock will generally include at least one alkane containing from1 to 4 carbon atoms and, more preferably, comprises methane or naturalgas with sulfur species removed and oxygen in premixed blends in ratiosof about 2:1 to about 20:1 CH₄ to O₂. The feed may in addition includeother species including nitrogen, carbon dioxide, carbon monoxide andwater, for example.

The composition, referred to herein as a catalyst, may be maintained inthe reaction zone as fixed, moving or fluidizing beds of solids. Afluidized bed operation is believed preferred because of its suitabilityin handling highly exothermic reactions like those involved in theoxidative coupling of methane.

The source of tin is believed to be extremely important. It is preferredto employ tin (II) acetate which contains a relatively large amount ofexcess acetic acid, e.g., the tin (II) acetate contains between about5-15% acetic acid. One such tin acetate can be purchased from AlphaProducts.

The tin-containing compositions of the invention which additionallyinclude other components such as a Group IIA metal, oxygen and/or aGroup IIIB, for example, can be prepared by process involving intimatelymixing tin(II) acetate having a stoichiometric excess of acetic acidwith an oxygen-containing compound of the Group IIA metal and/or anoxygen-containing compound of the Group IIIB metal, respectively.

In the case of the tin-containing compositions of the invention whichalso contain barium and oxygen or yttrium, barium and oxygen, such asmay be use in oxidative coupling, a preferred method of preparationincludes physically mixing tin (II) acetate with barium hydroxide oryttrium carbonate and barium hydroxide, respectively, and physicallygrinding the individual compounds together prior to calcining themixture to a selected temperature. One skilled in the art and guided bythe teachings herein may make appropriate calcining temperatureselections without undue experimentation.

Another preferred method comprises preparing the yttrium, barium andtin-containing catalyst of the invention in the substantial absence ofcarbon oxides, such as under a nitrogen or purified air or other inertatmosphere. Best results may be achieved when both carbonates and CO₂are prevented from contacting the catalyst during the early stages ofpreparation. A benefit of this procedure is believed to be catalystswith less variation in performance particularly when prepared in theabsence of CO₂, such as which is normally present in air.

The following examples illustrate the practice of the invention. It isto be understood that all changes and modifications that come within thespirit of the invention are desired to be protected and thus theinvention is not to be construed as limited by these examples.

EXAMPLES Example 1

Method of composition preparation:

Composition A

Tin (II) acetate, Sn(C₂ H₃ O₂)₂ (15.0 g, 0.06335 mole, from AlphaProducts) was mixed with yttrium carbonate, Y₂ (CO₃)₃ -3H₂ O (4.12 g,0.01 mole) and barium hydroxide, Ba(OH)₂ -8H₂ O (12.74 g, 0.0404 mole)with a mortar and pestle. The solids were ground to a fine powder tohomogenize these composition precursors. The hydroscopic nature of thesolids resulted in the production of a white slurry upon grinding. Afterthe slurry was thoroughly mixed, it was placed in a calcining furnaceand heated to 700° C. at a rate of 4° C./min after which it was slowlyheated to 800° C. at a rate of 2° C./min where in was held for fivehours. The furnace was purged with a flow of air. The solid remainedwhite after calcination. The preparation had a targeted composition ofYBa₂ Sn₃ O_(y).

Comparative Composition X1

Barium oxide, BaO (46.47 g, 0.303 mole); yttrium oxide, Y₂ O₃ (16.95 g,0.0751 mole) and tin oxide, SnO (60.92 g, 0.452 mole) were mixed with amortar and pestle. The powders were ground together for several minutesuntil they formed a homogeneous mixture. The mixture was then pelletizedinto a one inch diameter tablet and calcined in air using a claycrucible by placing the crucible in a calcining furnace and heated from27° C. to 400° C. at a rate of 2° C./min, held at 400° C. for one hour,then heated to 800° C. at a rate of 2° C./min and held at 800° C. forfive hours. It was then allowed to cool to room temperature.

The preparation had a targeted composition of YBA₂ Sn₃ O_(y).

Comparative Composition X2

Barium hydroxide, Ba(OH)₂ -8H₂ O (57.36 g, 0.1818 mole); yttriumcarbonate, Y₂ (CO₃)₃ -3H₂ O (18.54 g, 0.045 mole) and tin oxalate, SnC₂O₄ (56.04 g, 0.271 mole) were mixed with a mortar and pestle. Aftermixing for several minutes the waters of hydration resulted in theformation of a damp, yellowish paste. The paste material was transferredto a clay crucible for calcination in air. The same calcination programas described above for Comparative Composition X1 was used.

The preparation had a targeted composition of YBa₂ Sn₃ O_(y).

Comparative Composition X3

Barium hydroxide, Ba(OH)₂ -8H₂ O (19.12 g, 0.0606 mole); yttriumcarbonate, Y₂ (CO₃)₃ -3H₂ O (6.18 g, 0.015 mole) and tinethyleleglycoxide, SnO₂ C₂ H₄ (16.16 g, 0.0904 mole) were mixed with amortar and pestle. After mixing for several minutes a tan-coloredhomogenous mixture which maintained a powder consistency was formed. Thepowder mixture was transferred to a clay crucible and calcined in air.

The preparation had a targeted composition of YBa₂ Sn₃ O_(y).

Comparative Composition X4

Barium oxide, BaO (46.47 g, 0.303 mole); yttrium oxide, Y₂ O₃ (16.95 g,0.0751 mole) and tin (IV) oxide, SnO₂ (67.90 g, 0.4506 mole) were mixedwith a mortar and pestle. The powders were ground together to form ahomogenous grey powder which was transferred to a clay crucible andcalcined by heating from 27° C. to 700 ° C. at a rate of 4° C. /min,held at 700° C. for one hour, then heated to 800° C. at a rate of 2°C./min and held at 800° C. for five hours. It was then allowed to coolto room temperature.

The preparation had a targeted composition of YBa₂ Sn₃ O_(y).

Discussion

FIG. 1 presents the Sn(MNN) Auger spectra of Composition A andcomparative compositions X1-X4. As is evident from FIG. 1, althoughComposition A of the invention and the comparative tin-containingcompositions X1-X4 all had a targeted composition of YBa₂ Sn₃ O_(y), thetin Auger line transition of the composition of the invention is readilydiscernible from those of the comparative examples as the comparativeexample compositions exhibit two peaks, with the areas under each ofthese peaks being of about the same order of magnitude whereas thecomposition of the invention (Composition A) exhibits an Auger spectrumwherein the area under the M₅ N₄,5 N₄,5 transition peak greatly exceedsthe area under the M₄ N₄,5 N₄,5 transition peak.

Composition A of the invention has been found to be generally superiorto comparative compositions such as X1-X4 in terms of C₂ + hydrocarbonyield for the oxidative coupling of methane, when run under similaroxidative coupling conditions, e.g., a reaction temperature of about750° C. to about 850° C. and a methane-to-oxygen feed ratio rangingbetween about 2:1 to about 10:1.

Example 2

Compositions B-E were each prepared following the same generalprocedure, a different calcining regime (as described below), however,was used for each of the compositions B-E.

Tin (II) acetate, Sn(C₂ H₃ O₂)₂ (10.17 g, 0.0423 mole) and bariumhydroxide, Ba(OH)₂ -8H₂ O (13.16 g, 0.0423 mole) were mixed with amortar and pestle. The solids were ground to a fine powder to homogenizethe precursors and after several minutes of mixing, the waters ofhydration resulted in the formation of a creme-colored paste. This pastewas then apportioned into four (4) alumina crucibles and was allowed toset and dry for a period of several hours, during which time the pastematerial hardened resulting in the creation of a dark metallic color atthe material surface. Each of the crucibles were in turn subsequentlyplaced in a calcining furnace and calcined using the described calciningregime:

B - Heated from 27° C. to 200° C. at a rate of 4° C./min. Held at 200°C. for 12 hours and then allowed to cool to room temperature.

C - Same as B but now heated to a temperature of 400° C.

D - Same as B but now heated to a temperature of 600° C.

E - Same as B but now heated to a temperature of 800° C.

Discussion

FIG. 2 presents the Sn (MNN) Auger spectra of compositions B-E. Each ofthese compositions has a peak at 424.5 eV±1 eV, with this peak havingabout a 6 eV FWHM. Table I, below, reports the ratio of the area of theM₅ N₄,5 N₄,5 transition peak at 424.5 eV±1 eV to the area of the M₄ N₄,5N₄,5 transition peak at 430.5 eV±1 eV, for the Sn(MNN) Auger spectra ofthese compositions.

                  TABLE I                                                         ______________________________________                                                   Area of M.sub.5 N.sub.4,5 N.sub.4,5 transition peak                Compositions                                                                             Area of M.sub.4 N.sub.4,5 N.sub.4,5 transition                     ______________________________________                                                   peak                                                               B          333                                                                C          111                                                                D           33                                                                E           15                                                                ______________________________________                                    

For each of these compositions, the tin Auger line transition exhibits aratio of the area of the M₅ N₄,5 N₄,5 transition peak at 424.5 eV±1 eVto the area of the M₄ N₄,5 N₄,5 transition peak at 430.5 eV±1 eVexceeding 10 to 1.

In fact, those of these compositions which were calcined at lowertemperatures such as 600° C., 400° C. and 200° C., as in compositions D,C and B, respectively, exhibit peak area ratios substantially greaterthan 10 to 1, ranging up to about 350 to 1. Thus, for such compositions,the calcining temperature utilized in the preparation of the compositionappears related to the area ratio of the M₅ N₄,5 N₄,5 transition peak tothe M₄ N₄,5 N₄,5 transition peak for tin.

Example 3

Method of composition preparation

Composition A

The preparation of composition A is described above in Example 1.

Composition F

Same as that of composition A.

Compositions G and H

Same as A but now heated to a calcining temperature of 900° C. and 1000°C., respectively.

Discussion

FIG. 3 represents the Sn (MNN) Auger spectra of compositions A and F-HTable II, below, reports the ratio of the area of the M₅ N₄,5 N₄,5transition peak at 424.5 eV±1 eV to the area of the M₄ N₄,5 N₄,5transition peak at 430.5 eV±1 eV, for the Sn(MNN) Auger spectra of thesecompositions.

                  TABLE II                                                        ______________________________________                                                   Area of M.sub.5 N.sub.4,5 N.sub.4,5 transition peak                Compositions                                                                             Area of M.sub.4 N.sub.4,5 N.sub.4,5 transition                     ______________________________________                                                   peak                                                               A          132                                                                F          71                                                                 G          49                                                                 H          37                                                                 ______________________________________                                    

As with compositions B-E in Example 2, the compositions A and F-H eachexhibit a tin Auger line transition wherein the ratio of the specifiedpeak areas exceed 10. This is in contrast to the spectra of compositionsX1-X4 of Example 1 and FIG. 1 wherein this ratio is below 10 and the Sn(MNN) Auger spectra of oxidized tin shown in FIGS. 8-13 wherein thisratio generally ranges from about 4.8 to about 2.2.

Example 4

Composition A of Example 1 was placed in a 9 mm internal diameter quartztube reactor having a 3 mm outside diameter quartz thermowell. Apremixed gas blend containing 40% by volume of methane, 4% by volume ofoxygen and an inert carrier was employed. Nitrogen was used as aninternal standard for conducting mass balances. 40-60 Mesh quartz(Vycor) was used to dilute the 14-40 mesh catalyst loading to obtain amore nearly isothermal bed. A relative feed rate of 1000 cc standard (atroom temperature and pressure) of feed per hour per gram of catalyst wasemployed. Product gases were recycled to the front of the reactor andcombined with fresh feed at a ratio of about 10:1 recycle to fresh feed.Methane conversion was determined by differences in outlet and inletmolar rates and also by moles of products formed. Oxygen was nearlycompletely consumed (98%+) for temperatures of from 600° to 750° C. C₂ +selectivity improved with increasing temperatures and reached about 50%at 750° C. The only other major carbon-containing product was CO₂.

Example 5

Composition A of Example 1 was retested following the method of Example4 at a fixed temperature of 750° C. and relative feed rates (feedrate/catalyst weight) of about 5, 10 and 15 times that used in Example4. Even at these increased feed rates, oxygen consumption remained high(92-98%). C₂ + selectivity was relatively insensitive to thesevariations.

Example 6

Composition A of Example 1 was tested at higher feed rates andtemperatures, without recycling product gases. The feed composition wasalso varied. The reaction conditions are summarized below in Table III.

                  TABLE III                                                       ______________________________________                                                           Space Velocity                                             Run    CH.sub.4 :O.sub.2                                                                         (cc/gm-hr)  Max Temp, °C.                           ______________________________________                                        1       2:1        24,000      750                                            2      10:1        42,000      850                                            3      10:1        48,000      875                                            ______________________________________                                    

The first run showed little catalyst performance change over a 20 hourtesting cycle. The feed was changed to a higher CH₄ :O₂ ratio for runs 2and 3. At 850° C. in run 2, selectivity to C₂ + reached about 68% withCO₂ making up most of the balance. Even at the high relative feed rates,near full oxygen conversion was observed. In run 3, both temperature andfeed rate were increased. The catalyst began to change significantly at875°. When the temperature was lowered to 850° C. after having been at875° C., the catalyst showed a significant loss in C₂ + selectivity.

Example 7

Bulk metals analysis of fresh and used Y₁ Ba₂ Sn₃ O_(y) catalystprepared by the method of Composition A of Example 1 was conducted usingx-ray fluorescence (XRF). The results are listed below in Table IV. Ascan be seen, for samples 1 and 2, the Ba and Sn ratio and the elementalcompositions for all three elements are within 10% of the fresh catalystcomposition. For example 3, a correction must be applied due to theprobable effect of the catalyst bed diluent used in the reactor test.Using the yttrium elemental analysis to estimate diluent amount, onemust multiply the analyses by about 1.5 to get corrected value. Afterdoing so, the Sn value is within 10% of the fresh catalysts and the Bavalue within 15% of the fresh catalyst value. Thus, large, i.e. greaterthan 20%, losses of the elements are not observed with use.

                  TABLE IV                                                        ______________________________________                                        Sample   % Y      % Ba    % Sn     Stoichiometry                              ______________________________________                                        1 (used) 9.5      31      34       Y.sub.1 Ba.sub.2.1 Sn.sub.2.68             2 (used) 9.9      33      39       Y.sub.1 Ba.sub.2.16 Sn.sub.2.95            3 (used) 6.4        18.2    22.5   Y.sub.1 Ba.sub.1.84 Sn.sub.2.63            4 (fresh)                                                                              9.6      32      37       Y.sub.1 Ba.sub.2.16 Sn.sub.2.89            ______________________________________                                    

As expected, the tin is lower than targeted due to the presence ofexcess acetate in the tin acetate starting material. Not much differencewas observed between some of the used catalyst and fresh catalystindicating no large-scale metal leaching or volatilization.

Example 8

Y₁ Ba₂ Sn₃ O_(y) catalyst (50 mg), prepared by the method of CompositionA of Example 1, was crushed to 80-100 mesh and diluted 15:1 with aluminaand evaluated to determine oxygen conversion as a function of catalyticcontact time (weight of catalyst per flow rate of gas feed) andtemperature. Tests were conducted at 5 psig outlet and feed compositionof 40% methane+4% oxygen+56% nitrogen. The tests were conducted in theorder of lowest to highest temperature. Standard conditions (750° C., 5psig, 25 sccm=0.120 g catalyst-sec/cc feed at STP) were repeated aftereach temperature to assure that catalyst performance remained unchanged.The results are set forth in Table V below.

                  TABLE V                                                         ______________________________________                                        Repeat of Standard Conditions (750° C., 5 psig, 0.12 g                 cat-sec/cc, 56% N.sub.2 + 40% CH.sub.4 + 4% O.sub.2)                                          % Oxygen  % C.sub.2 +                                         Condition       Conversion                                                                              Selectivity                                         ______________________________________                                        Start-of-Run    88        55                                                  750° C.                                                                After Running   88        54                                                  at 775° C.                                                             After Running   86        53                                                  at 800° C.                                                             After Running   89        54                                                  at 825° C.                                                             After Running   87        52                                                  at 875° C.                                                             ______________________________________                                    

At 750° C., C₂ + selectivity was relatively insensitive to oxygenconversion until reaching complete conversion, upon which C₂ +selectivity began to drop dramatically.

At 800° C., C₂ + selectivity declines as contact time increases, even atoxygen conversions of less than 100%. At the end of the run with 0.05 gof catalyst, C₂ + selectivity had declined about 65% at a contact timeof 0.012 g catalyst-sec/cc gas.

At 850° C., C₂ + selectivity drops dramatically as contact time isincreased.

Example 9

Three samples of Y₁ Ba₂ Sn₃ O_(y) catalyst, A', A" and A'",respectively, were prepared by the method of Composition A of Example 1except the calcination temperatures of A" and A'" were 1100° C. and1550° C., respectively. Catalyst A' was calcined at 800° C. as inExample 1. Testing of these three catalysts under the same conditions of250 mg catalyst, 100 standard cc per minute of a preblended gascontaining about 15% CH₄, 7.5% O₂, and balance N₂, at 750° C. gave theperformance shown in Table VI.

                  TABLE VI                                                        ______________________________________                                                 Conversion %     % C.sub.2 +                                         Catalyst O.sub.2      CH.sub.4                                                                              Selectivity                                     ______________________________________                                        A'       95           27      22                                               A"      100          29      20                                               A'"     20            5       0                                              ______________________________________                                    

For best performance in oxidative coupling, the catalysts should becalcined below 1550° C. and preferably at less than 1100° C.

Example 10

The effects of varying methane-to-oxygen ratio on performance of thecatalyst of Composition A of Example 1 was investigated in a plug-flowreactor using 50 mg of catalyst at 5 psig, 100 sccm CH₄, 0 or 135 sccmN₂ which corresponds to 0% or 56% at nitrogen dilution, respectively, atboth 750° C. and 800° C. The results are summarized in Tables VII andVIII below.

                  TABLE VII                                                       ______________________________________                                        Effect of Varying Methane-to-Oxygen Ratio on                                  Performance with Y.sub.1 Ba.sub.2 Sn.sub.3 O.sub.y  at 750° C.                          Methane-to-Oxygen Ratio                                                       5:1    10:1    18:1                                          ______________________________________                                        % Conversion                                                                                 56% N.sub.2 Dilution                                                                       33     42    57                                   O.sub.2                                                                                     w/o N.sub.2  49     62    77                                                   56% N.sub.2 Dilution                                                                       5.2    4.5   4.2                                  CH.sub.4                                                                                    w/o N.sub.2  8.7    6.7   5.2                                   % Selectivity                                                                                56% N.sub.2 Dilution                                                                       42     54    62                                   C.sub.2 +                                                                                   w/o N.sub.2  38     52    64                                                   56% N.sub.2 Dilution                                                                       0.9    1.3   1.6                                  C.sub.3 +                                                                                   w/o N.sub.2  1.2    1.9   2.3                                    C.sub.2 H.sub.4 to                                                                          56% N.sub.2 Dilution                                                                       0.19    0.17                                                                               0.16                                 C.sub.2 H.sub.6 ratio                                                                       w/o N.sub.2  0.41   0.34  0.29                                  ______________________________________                                    

                  TABLE VIII                                                      ______________________________________                                        Effect of Varying Methane-to-Oxygen Ratio on                                  Performance with Y--Ba--Sn--O Catalyst at 800° C.                                       Methane-to-Oxygen Ratio                                                       5:1    10:1    18:1                                          ______________________________________                                        % Conversion                                                                                 56% N.sub.2 Dilution                                                                       59     74    89                                   O.sub.2                                                                                     w/o N.sub.2  83     93    99                                                   56% N.sub.2 Dilution                                                                       12.7   10.2  7.6                                  CH.sub.4                                                                                    w/o N.sub.2  16.4   11.7  7.8                                   % Selectivity                                                                                56% N.sub.2 Dilution                                                                       57     68    74                                   C.sub. 2 +                                                                                  w/o N.sub.2  53     67    76                                                   56% N.sub.2 Dilution                                                                       3.0    3.4   3.1                                  C.sub.3 +                                                                                   w/o N.sub.2  3.5    4.6   4.3                                    C.sub.2 H.sub.4 to                                                                          56% N.sub.2 Dilution                                                                       0.49    0.40                                                                               0.31                                 C.sub.2 H.sub.6 ratio                                                                       w/o N.sub.2  0.94   0.68  0.50                                  ______________________________________                                    

The data show that methane-to-oxygen ratios and temperature havesignificant impacts on conversion and selectivity. On the other hand,nitrogen dilution has little effect on C₂ + selectivity and appears toplay a secondary role on conversion, presumably a kinetic rate effect,from altering reactant partial pressures. As the methane-to-oxygen ratioincreases, methane conversion decreases whereas C₂ + selectivityincreases. The yield of C₂ + hydrocarbons is simply the product ofselectivity and conversion. The C₃ + selectivity was slightly higherwithout nitrogen dilution.

EXAMPLE 11

Y₁ Ba₂ Sn₃ O_(y) catalyst prepared by the method of Composition A ofExample 1 was analyzed by XPS to determine metal ratios and oxidationstates. Surface compositions, atomic ratios and electron bindingenergies (ebe's) are reported in Tables IX-XI.

                  TABLE IX                                                        ______________________________________                                        Relative Atomic Percent of Y.sub.1 Ba.sub.2 Sn.sub.3 O.sub.y Catalyst         Run     O      .sup.C total                                                                            .sup.C CO.sub.3                                                                     Y      Ba  Sn                                  ______________________________________                                        1       50.8   10.7      1.6   14.7   8.8 14.9                                2       47.5   25.1      3.8    8.0   6.4 13.0                                3       55.6    6.1      1.2   10.8   9.9 17.6                                ______________________________________                                    

                  TABLE X                                                         ______________________________________                                        XPS Surface Stoichiometry                                                     Target             Experimental                                               Run      Y     Ba        Sn  Y      Ba   Sn                                   ______________________________________                                        1        1     2         3   1      0.60 1.00                                 2        1     2         3   1      0.79 1.62                                 3        1     2         3   1      0.93 1.64                                 ______________________________________                                    

                  TABLE XI                                                        ______________________________________                                        Electron Binding Energies (eV) of Y.sub.1 Ba.sub.2 Sn.sub.3 O.sub.y           Catalyst                                                                      ______________________________________                                        Run     0 1s   %       C 1s %      Y 3d5/2                                                                              %                                   ______________________________________                                        1       528.1  65      284.6                                                                              85     156.4  100                                         530.5  35      288.8                                                                              15                                                2       528.8  50      284.6       156.2  100                                         531.0  50      288.3                                                  3       529.3  60      284.7                                                                              61     156.4  100                                         531.3  40      285.9                                                                              17                                                                       289.5                                                                              22                                                ______________________________________                                        Run      Ba 3d5/2 %          Sn 3d5/2                                                                             %                                         ______________________________________                                        1        778.0    100        483.7   20                                                                    485.6   80                                       2        778.2    100        485.4  100                                       3        778.6    100        485.9  100                                       ______________________________________                                    

Repeat analyses on three portions of the sample gave variablecompositions (Table IX) indicating heterogeneity of the fresh catalyst.Yttrium surface enrichment, as indicated by the Sn/Y and Ba/Y ratios ofTable X, causes the Y:Ba:Sn ratios to differ from the target bulk value1:2:3. The ratios obtained from the three samples vary slightly; yet,they reflect barium and tin depletion. Note, for instance, that thefirst run in Table X has a stoichiometry consistent with the tinpyrochlore (Y₂ Sn₂ O₇) which has been identified by X-ray diffraction(XRD). Tin is present in two or three chemical states, Sn 3d 5/2 ebe'sof 483.7 eV and 485.6 eV indicates elemental tin (20%) and Sn⁺² and/orSn⁺⁴ (80%), respectively (Table XI). This result is in excellentagreement with XRD data. Only one portion of the three analyzedcontained elemental tin. This could be indicative of tin oxidation orsample heterogeneity. The Sn 3d ebe's are usually low when compared toliterature and experimental XPS data of the pure compounds, indicatingthat tin formed a compound with yttrium and barium. The Ba 3d 5/2 of778.2 eV is too low to indicate the presence of BaCO₃ and BaO (ebe's779.0 and 779.7 eV, respectively) as reported in Table XI. Y 3d ebe's ofall samples were at 156.5±0.3 eV. Literature reports the same values forY₂ O₃. Two oxygen species with ebe's at approximately 528.1 and 530.0 eVwere found. The former species is typical for metal oxides. The latteris too low for adsorbed oxygen and could be representative for thespecific compound formed by barium, tin and yttrium.

Example 12

A portion of a sample of the catalyst of Composition A of Example 1 wasmounted on a scanning electron microscope (SEM) stub. In addition,another portion of sample was embedded in epoxy and the cross-sectionexposed by grinding and polishing and also by cutting the embeddedsample with a diamond knife on the ultramicrotome. The sample was thenexamined in the SEM uncoated, and subsequently coated with gold in thevacuum evacuator. At X10,000 magnification, the areas examined of theuncoated sample show grainy particles ranging in size from 500 Å to 3000Å in diameter. Some of the crystals appeared to be orientedperpendicular to the plane of the other crystals.

SEM-EDX elemental analysis dot maps were obtained of the cross-sectionareas. Y and Ba appear uniformly distributed, but the Sn rich areasappear to be concentrated in small clumps throughout the sample.

Example 13

A long term stability test was conducted in a recycle reactor whereinthe reactor gases were well backmixed with 50 mg of the Y₁ Ba₂ Sn₃ O_(y)catalyst of Composition A of Example 1 at 750° C., 3 psig and 120,000cc/gm-hr SV of 40% CH₄ +4% O₂ +56% N₂. The run lasted nearly 10 dayswithout any change in selectivity or conversion, other than thataccountable by changing feed gas cylinders. Studies of the used catalystare described below.

Studies have shown that there are several characteristics of such Y₁ Ba₂Sn₃ O_(y) metal oxide catalysts that classify it as a uniquecomposition. STEM/EDX characterization showed a distinct change in thehomogeneity of the composition throughout the used catalyst compared tofresh catalysts. Depending on the reaction conditions, varying degreesof homogeneity could be obtained with the most homogeneous samples beingproduced under total oxygen conversion or above 875° C. When coupledwith XRD analysis, the STEM/EDX data present a model of the catalystbeing a crystalline barium stannate (BaSnO₃) which is coated or in solidsolution with an amorphous oxide/carbonate mixture of yttrium andbarium, represented by YBaC_(z) O_(y). The resulting mixture is unique.

To illustrate this increase in homogeneity of the used catalyst, thecomposition at several points in the catalyst, as determined bySTEM/EDX, was plotted on a ternary phase diagram. In FIGS. 4-7, YO₁.5,BaO, and SnO₂ are at the three corners and the composition at any pointin the diagram can be determined where the point intersects the tielines for each of the elements. The tie lines are in the units of mole%. For example, a composition represented by the point in the phasediagram that intersects the 30% line of BaO, the 20% line of YO₁.5 andthe 50% line of SnO₂ has 30 mole % BaO, 20 mole % YO₁.5 and 50% SnO₂, orY₁ Ba₁.5 Sn₂.5.

Referring to the drawings, FIG. 4 is a STEM/EDX ternary phase diagram ofthe distribution of compositions observed in the fresh Y₁ Ba₂ Sn₃ O_(y)catalyst. A large degree of scatter indicates the heterogeneity of thecatalyst. Virtually pure BaO, Y₂ O₃ and SnO₂ were observed along withmixtures of the three metal oxides.

FIG. 5 is a STEM/EDX ternary phase diagram of a used catalyst that hasnot been exposed to reducing conditions.

A majority of the compositions falls on the tie line between BaSnO₃ andYO₁.5 and the region below it. Many areas converge around the Y₁ Ba₂ Sn₃O_(y) nominal composition even though there is no crystalline phase withthis composition. BaSnO₃ is the major phase in this material with minoramounts of SnO₂ which are also observed by STEM/EDX. The only way areascan have a composition of Y₁ Ba₂ SnO₃ is to have an amorphous coating orsolid solution of yttria, barium, carbonates and tin oxides oncrystalline BaSnO₃.

FIG. 6 is a ternary phase diagram of a catalyst that has been exposed toreducing conditions (100% O₂ conversion) at 750° C. The homogeneity ofthe composition has increased in this sample such that most areas falljust below the BaSnO₃, YO₁.5 tie line and in closer proximity to thecrystalline phase so the majority of the areas contain a crystallineBaSnO₃ which is coated or in solid solution with an amorphousoxide/carbonate mixture of yttrium and barium.

FIG. 7 is a STEM/EDX ternary phase diagram of a catalyst that has beenexposed to severe reducing conditions. Extreme reducing conditions at875° C. further homogenized the catalyst composition as seen in FIG. 4.The distribution centers exclusively on the Y₁ Ba₂ Sn₃ O_(y) compositioneven though by XRD, the major crystalline phase is BaSnO₃.

The region of the phase diagram that the composition of the usedcatalyst falls in is:

    (BaO).sub.a (YO.sub.1.5).sub.b (SnO.sub.2).sub.c

wherein 5%<a<50%; 0%<b<57%; and 25%<c<90%.

Depending upon the catalyst preparation, XPS analysis of the catalystindicates apparent enrichment of the surface with either barium in theform of carbonate or oxide or yttria. Smaller amounts of tin weredetected on the surface in part due to the Sn aggregating into smallSnO₂ particles. Auger line shape analysis of the Sn MNN transition ofthe fresh catalyst indicates the Sn is in a unique environment.Unusually high hydrogen consumption was observed in the TPR/TPO analysisof Y₁ Ba₂ Sn₃ O_(y) catalyst along with trends in reduction temperatureversus catalyst activity. All of these unique characteristics aredescribed more fully in the following examples.

Example 14

Analytical electron microscopy shows distinct differences in fresh andused Y₁ Ba₂ Sn₃ O_(y) catalysts which evidence the unique nature of thematerial. A histogram of selected areas were analyzed in both the freshand used catalysts by Energy Dispersive X-Ray (EDX) in the STEM mode.After calibrating with known standards, the metal composition could bequantitated in these different areas. A fresh catalyst was veryheterogeneous in composition with regions of pure BaCO₃, SnO₂ and Y₂ O₃observed along with mixtures of the various elements. Depending on thereaction conditions, the catalyst becomes more homogeneous in Y, Ba andSn composition. Severe reaction conditions such as total oxygenconversion and greater than 875° C. reaction temperatures cause the mostdramatic changes and also caused the catalyst to lose selectivity to C₂+. Virtually all particles analyzed had close to the nominal compositionY₁ Ba₂ Sn₃ O_(y). This is unusual in that the XRD showed only BaSnO₃ asthe major phase. Therefore, it is believed that the catalyst may becharacterized as an amorphous/crystalline mixture where the onlysignificant crystalline phase is BaSnO₃ and the amorphous phase is aYBaO_(x) oxide which homogeneously coats or forms a solid solution withthe BaSnO₃. The composition of BaSnO₃ and YBaO_(x) phases forms auniquely uniform material.

Less severe conditions also caused the catalyst to become morehomogeneous in composition yet still retain its selectivity to C₂ +hydrocarbons. For example, at 97% oxygen conversion, 800° C., 5:1 CH₄/O₂ feed at 120,000 cc/gm-hr space velocity (SV) and 4 hours reactiontime, a large fraction of the areas had a composition near Y₁ Ba₂ Sn₃O_(y). A majority of areas followed the tie line from BaSnO₃ to Y₂ O₃,indicating varying amounts of Y₂ O₃ are in solid solution or coating theBaSnO₃.

Elemental x-ray mapping of the used catalyst also confirmed thecompositional homogeneity of the catalyst.

High resolution TEM showed lattice fringes on the Y₁ Ba₂ Sn₃ O_(y)catalyst which had been used at full oxygen conversion. Atmagnifications greater than 1,000,000X, fringe spacings of 5.5 Å, 7 Åand 12.2 Å were observed. These are larger than pure BaSnO₃ at 4.117 Åand Y₂ Sn₂ O₇ at 10.4 Å. The expanded lattice seen in the TEM suggestsome small particles which have incorporated other materials into thelattice such as yttria, i.e., solid solutions. BaCO₃₀ has celldimensions of a=5.134 Å, b=8.9 Å and c=6.43 Å, some of which are similarto those observed by TEM.

All used catalysts show an increase in the homogeneity of composition,suggesting a unique mixture of crystalline and amorphous phase.

Example 15 X-Ray Diffraction Analysis

A sample of Y₁ Ba₂ Sn₃ O_(y) catalyst was calcined to 800° C. for 5hours in air which resulted in a complex mixture of barium carbonate(BaCO₃), tin oxide (SnO₂) and minor poorly crystalline phases of bariumstannate (BaSnO₃) and yttrium tin pyrochlore (Y₂ Sn₂ O₇). As shown inExample 17, below, Sn119 NMR chemical shifts suggested that neither theY₂ Sn₂ O₇ nor the BaSnO₃ were solid solutions. Further calcination to1100° C. increased the crystallinity and concentration of BaSnO₃ yetchanged the catalysts selectivity to more combustion products. Asignificant decrease in BaCO₃ was also observed at this temperature.Further calcination to 1400° C. caused the disappearance of BaCO₃ andthe major phases are now BaSnO₃ and a Ba(Y)SnO₃ solid solution which hasan expanded cell of 4.1354 Å. Pure Y₂ Sn₂ O₇ was also present. Thematerial stayed with this composition until the calcining temperaturewas close to 1700° C. at which the sample melted and reacted with thealumina crucible. SnO₂ observed in fresh catalysts had a preferredorientation such that the 101 and 202 XRD diffraction intensities weremuch greater than the intensities published in the powder diffractionfiles. Bulk SnO₂ prepared by calcination of the Sn(II) acetate startingmaterials also has the preferred orientation shown by the 101 and 202reflection intensity enhancement. This feature is common to theoxidative coupling catalysts but is also found in SnO₂, a combustioncatalyst prepared from tin acetate.

Depending on the reaction conditions, the used catalysts hadsignificantly higher crystallinity and were more pure in BaSnO₃ than thefresh catalysts. The catalyst was in effect being crystallized to BaSnO₃by being used for methane oxidative coupling. The higher the oxygenconversion, the larger the effect on the catalyst. For that matter,catalysts that had been heated too hot or run under reducing conditions(100% oxygen conversion) were some of the most crystalline with themajor phase being pure BaSnO₃ along with minor phases of Y₂ Sn₂ O₇ solidsolution, SnO₂, and another poorly crystalline BaSnO₃ solid solutionphase. Barium carbonate, which was a major phase in the fresh catalysthad decomposed to form BaSnO₃ in the catalyst used at full oxygenconversion. BaCO₃ only exists in traces in the used catalyst. The amountof carbonate in the used catalysts depends on the severity of operation.The solid solution of Y₂ Sn₂ O₇ had an expanded cubic cell constant of10.430(4) Å compared to the known value of 10.373 Å. The minor phase ofBaSnO₃ solid solution had a cubic cell constant of 4.1209 Å compared tothe known cell constant of 4.1163 Å. Expansion of the unit cell in boththe Y₂ Sn₂ O₇ and BaSnO₃ is caused by yttria substituting for thesmaller tin ion in the structure, thus creating a solid solution withyttria.

Example 16 XPS/Auger Analysis

Both fresh and used Y₁ Ba₂ Sn₃ O_(y) catalysts (fresh and usedCompositions A of Example 1) were analyzed by Auger spectroscopy whichuncovered an unusual phenomena with the fresh catalyst's Sn MNN Augertransition. Typical Sn MNN transitions observed with SnO (FIG. 10), SnO₂(FIG. 11), BaSnO₃ (FIG. 12), and Y₂ Sn₂ O₇ (FIG. 13) shows both a M₄N₄,5 N₄,5 and a M₅ N₄,5 N₄,5 transition; whereas, in the fresh Y₁ Ba₂Sn_(O) ₇ catalyst (Composition A of Example 1) (FIGS. 1 and 3), the M₄N₄,5 N₄,5 is rapidly quenched, i.e., it is not readily observed. SnO₂,prepared from the acetate, which has the unusually intense 101 and 202XRD diffractions, has both the M₄ N₄,5 N₄,5 and M₅ N₄,5 N₄,5 transitionsas does bulk SnO₂. Thus, the comparative absence of the M₄ N₄,5 N₄,5peak in the YBa₂ Sn₃ O_(y) composition of the invention does not appearto be due to the preferred orientation of the SnO₂ particles.

With respect to the XPS results, the binding energy shifts for freshcatalyst were consistent with the XRD results that showed the presenceof Y₂ O₃ and SnO₂. The optimized preparation using tin acetate had largeamounts of BaCO₃ on the surface, whereas a preparation involvingphysically mixed pure oxides had Sn metal and a barium oxide with lowbinding energy shift of 778.2 eV. Pure BaCO₃ and BaO have bindingenergies of 779.0 and 779.7 eV. Low binding energies are also observedin the new superconductive Y₁ Ba₂ Cu₃ O_(y) where the barium is alayered perovskite structure.

Relative surface compositions were determined and found to be dependenton catalyst preparation. The preferred method of synthesis using tinacetate had an apparent surface enrichment of barium in the form of bothcarbonate and oxide and a depletion of tin when calcined to 800° C.Depth profiling showed that the composition was homogeneous throughoutthe bulk which suggests that the tin is in small (<2000 Å) crystalliteswhich make it appear to be in lower concentration by XPS. Catalystprepared by physically mixing Y₂ O₃, BaO and SnO and calcining to 800°C. had a surface enrichment of yttria and a depletion of barium and tin.Both catalysts had similar performance for methane oxidative coupling.The used catalyst prepared from tin acetate still had barium enrichmentif reaction conditions were maintained below 100% oxygen conversion. Aused catalyst that had been exposed to extreme reaction conditions suchas 875° C. had yttria enrichment.

The Auger line shapes of fresh and overreduced catalyst are best shownin FIG. 8 (same as shown in FIGS. 1 and 3 for Composition A of Example 1but now shown without other spectra) and FIG. 9 respectively. As shown,the used catalyst (see FIG. 9) contains a 430.5 eV±1 eV peak ("secondpeak") of sufficient size relative to the 424.5 eV±1 eV peak ("firstpeak") that the ratio of the first peak to the second peak is not atleast 10 to 1. In fact, for the Auger spectrum shown in FIG. 9, theratio of these peak areas is more in the range of 8 to 1.

Example 17 Sn119 Solid State NMR

NMR analysis of fresh Y₁ Ba₂ Sn₃ O_(y) catalyst showed, that at thesensitivity of NMR, only known tin compounds were in the fresh catalyst.When calcined to 920° C., SnO₂ and a fairly broad peak for BaSnO₃ wereobserved. In a good, non-over-reduced catalyst, the Sn119 NMR is onlyslightly different from the fresh catalyst. A small increase in theBaSnO₃ peak was observed in the used catalyst. An 1100° C. calcinationsharpened the BaSnO₃ peak, indicating better crystallinity, and a Y₂ Sn₂O₇ pyrochlore was the only other species present. Integrated areas underthese peaks corresponded well with XRD results in estimatingcompositions.

Example 18 Thermal Gravimetric Analysis

The fresh Y₁ Ba₂ Sn₃ O_(y) catalyst of Example 1 (Composition A) wascalcined to about 800°-1000° C. in air. The material showed a gradualweight loss of about one (1) weight percent when heated to 800°-900° C.Such a small weight loss is attributed to the catalyst desorbingmoisture or other volatile compounds adsorbed from the atmosphere andpossible evolution of CO₂ from BaCO₃ decomposition at about 800° C.Cooling back to room temperature in dry air did not cause the catalystto regain any of its lost weight.

Example 19

The catalyst of Example 1 (Composition A) was tested at 750° C. in arecycle reactor wherein the gases were well backmixed to illustrate theeffect of complete oxygen conversion on selectivity to C₂ +hydrocarbons. The feed was 10:1 CH₄ O₂ +56% nitrogen and the pressurewas held at 3 psig. Two experiments were conducted so as to obtain awide variation in contact time (grams of catalyst/sec/cc gas at STP):one with 0.5 gram catalyst and the other with 0.05 gram catalyst. Eachrun was made in the order of lowest to highest contact time. Selectivityto C₂ + hydrocarbons remains relatively constant until reaching acontact time of about 0.5 seconds; thereafter, C₂ + selectivitydecreases as contact time increases. Upon reaching the longest contacttime of 6, the initial contact time of 0.3 was repeated for the run with0.5 gram catalyst. The C₂ + selectivity returned to 45% which is 10%below the original value of 55%, implying catalyst deactivation. Part ofthe fall off in C₂ + selectivity at contact times about 0.5 isattributed to the intrinsic response of the catalyst at high oxygenconversion; however, part of the drop is an accumulative, nonreversibledecline from catalyst aging caused by reduction and degradation atcomplete oxygen conversion.

Example 20

A carbonate free Y₁ Ba₂ Sn₃ oxide catalyst was prepared by grindingY(NO₃)₃ ·6H₂ O (2.30 g), Ba(OH)₂ ·8H₂ O (3.79 g) and Sn(OCOCH₃)₃ (4.2 g)under air or nitrogen to form a soft paste. The paste was extruded andfired in air at 100° C., 200° C., 300° C., 400° C., 500° C., 600° C. and700° C. for 15-30 minutes at each temperature, then heated at 800° C.for 5 hours under air flow. The catalyst was then calcined at 900° C.for 1 hours, the temperature was reduce to 800° C. and the catalyst wascalcined at that temperature for 2 hours. X-ray diffraction of the freshcatalyst showed BaSnO₃ as major, Y₂ O₃ and BaCO₃ (Witherite phase) asintermediate, and SnO₂ as a minor crystalline material.

Example 21

The catalyst of Example 20 was ground and sieved to pass through a 180mesh sieve and be held on a 250 mesh sieve. 50 milligrams of thecatalyst, diluted with about 500 mg of alpha alumina, was tested with afresh feed blend of 30% CH₄, 6% O₂, 56% N₂ at 100 standard cc per minuterate at 800° C. Ultra high purity gases were used. In addition, 250cc/minute of the product gas at room temperature was recycled to thefront of the unit. Near complete oxygen conversion was obtained (97%)and 20% of the methane was converted. Carbon atom selectivities were 59%to hydrocarbons with 2 or more carbon atoms, 2% to carbon monoxide, and39% to carbon dioxide.

It is to be understood that the discussion of theory, such as thediscussion regarding quantum mechanics and the mechanics of Augerelectron spectroscopy, for example, are included to assist in theunderstanding of the subject invention and are in no way limiting of theinvention.

The foregoing detailed description is given for clearance ofunderstanding only, and no unnecessary limitations are to be understoodtherefrom, as modifications within the scope of the invention will beobvious to those skilled in the art.

What is claimed is:
 1. A method for converting a feedstock alkanecontaining from 1 to 4 carbon atoms to a higher molecular weighthydrocarbon, said method comprising:contacting a feedstock comprising atleast one alkane containing from 1 to 4 carbon atoms with an oxidativecoupling catalyst comprising: a) an oxidized Group IIA metal selectedfrom the group consisting of magnesium, calcium, strontium and barium;and b) oxidized tin wherein the tin and Group IIA metal are in anapproximate atomic ratio of 2-4 atoms of tin per 0.5-3 atoms of GroupIIA metal, with said catalyst having a tin Auger line transition whereinthe ratio of the area of the M₅ N₄,5 N₄,5 transition peak at 424.5 eV±1eV, having a 6 eV FWHM, to the area of the M₄ N₄,5 N₄,5 transition peakat 430.5 eV±1 eV is at least 10 to 1, in the presence of oxygen atoxidative coupling reaction conditions to produce a gaseous mixturecomprising hydrocarbon products having higher molecular weight than thefeedstock alkane from which they were formed.
 2. The method of claim 1wherein said catalyst composition is prepared by a method comprisingintimately mixing an oxygen-containing compound of said Group IIA metalwith tin (II) acetate having a stoichiometric excess of acetic acidfollowed by calcining the mixture to a selected temperature.
 3. Themethod of claim 1 wherein said catalyst composition additionallycomprises a Group IIIB metal selected from the group consisting ofyttrium, lanthanum and scandium, wherein the Group IIIB metal, Group IIAmetal and tin are present in an atomic ratio of approximately1:0.5-3:2-4, respectively.
 4. The method of claim 3 wherein said GroupIIA metal is barium, said Group IIIB metal is yttrium and wherein theyttrium, barium and tin are present in an atomic ratio of about 1:2:3,respectively.
 5. The method of claim 3 wherein said catalyst compositionis prepared by a method comprising intimately mixing oxygen-containingcompounds of each of said Group IIIB metal and Group IIA metal with tin(II) acetate having a stoichiometric excess of acetic acid followed bycalcining the mixture to a selected temperature.
 6. A method forconverting a feedstock alkane containing from 1 to 4 carbon atoms to ahigher molecular weight hydrocarbon, said method comprising:contacting afeedstock comprising at least one alkane containing from 1 to 4 carbonatoms with an oxidative coupling catalyst comprising: a) oxidizedyttrium; b) oxidized barium; and c) oxidized tin wherein the tin, bariumand yttrium are present in an approximate atomic ratio of 2-4 atoms oftin per 0.5-3 atoms of barium per atom of yttrium, said catalystcomposition having a tin Auger line transition wherein the ratio of thearea of the M₅ N₄,5 N₄,5 transition peak at 424.5 eV±1 eV, having a 6 eVFWHM, to the area of the M₄ N₄,5 N₄,5 transition peak at 430.5 eV±1 eVis at least 10 to
 1. 7. The method of claim 6 wherein the yttrium,barium and tin of said catalyst composition are present in anapproximate atomic ratio of about 1:2:3, respectively.
 8. The method ofclaim 6 wherein said catalyst composition is prepared by a methodcomprising intimately mixing yttrium carbonate and barium hydroxide withtin (II) acetate having a stoichiometric excess of acetic acid followedby calcining the mixture to a selected temperature.